In general, a semiconductor integrated circuit is provided with an input signal reception circuit. An input signal reception circuit changes a state of an output signal depending on a change in level of an input signal of minute amplitude that is given from outside (an external input signal). In general, a differential amplifier is used as such an input signal reception circuit for detecting a change in level of the external input signal.
A differential amplifier generally has two input terminals. Methods for detecting whether an input signal provided to a differential amplifier has reached a certain level are roughly divided into two types.
In a first method, one of the two input terminals is provided with an external input signal IN, while the other is provided with an inverted signal /IN of the external input signal IN, whereby the magnitudes of these two signals are compared.
In a second method, a reference voltage (a Reference signal) VREF having a fixed value is compared with an external input signal IN.
In the first method, circuitry characteristics such as an operation speed of the circuit can be improved, for example. However, an area of the circuit increases, and a power consumption thereof also increases.
In contrast, the second method uses only half of the wirings for the input signal of the first method. The second method therefore allows the area of the circuit to be reduced and also allows power consumption to be suppressed. However, the second method compares the output signal from outside with the reference voltage having a fixed value. Thus, due to asymmetry in the current mirror circuit, one of either the rising edge or the falling edge of the output signal has a blunted waveform with respect to the other, whereby a difference in transition time inevitably occurs. Then, even in an input signal reception circuit using the second method, symmetry between the rising edge and the falling edge of the output signal is maintained, and the difference in transition time is shortened as much as possible.